1. Field of the Invention
The present invention relates to a method of preparing formulations comprising a biologically active substrate or substance which is converted into a biologically substance.
2. Description of the Prior Art
The wettability and dissolution properties of a biologically active substance or substance which is converted thereinto in vivo such as a drug or drug precursor greatly influence the bioavailability of the drug or drug precursor. In many cases, very active drugs or drug precursors, for example, present a poor absorption profile because of their unfavourable dissolution characteristics. Such techniques as reducing the particle size of the drug and the addition of wetting agents have been widely appplied to obviate these problems. However, these techniques frequently prove to be not effective enough. Therefore much effort has been devoted to develop new formulations or new techniques to achieve better results. Considerable experimental work in this area has recently opened up two new research lines based on the preparation of "solid dispersions" and of "inclusion compounds". In the former approach the drug or drug precursor is molecularly dispersed in the carrier, usually a water-soluble polymer (S. Riegelman, W. L. Chiou 987,588 4/1976 Canada), while in the latter approach the drug or drug precursor forms molecular complexes with water-soluble cyclodextrins (J. Szejtli "Cyclodextrins and Their Inclusions Compounds", Akademia Viado, Budapest 1982). A need therefore continues to exist for a method and formulations by which the bioavailability of a biologically active substance or a substance convertible into a biologically active substance in vivo can be improved.